Human senescence

Toxicology of pharmaceutical and nutritional longevity compounds

Aging is the most prominent risk factor for many diseases, which is considered to be a complicated biological process. The rate of aging depends on the effectiveness of important mechanisms such as the protection of DNA from free radicals, which protects the structural and functional integrity of cells and tissues. In any organism, not all organs may age at the same rate. Slowing down primary aging and reaching maximum lifespan is the most basic necessity. In this process, it may be possible to slow down or stabilise some diseases by using the compounds for both dietary and pharmacological purposes. Natural compounds with antioxidant and anti-inflammatory effects, mostly plant-based nutraceuticals, are preferred in the treatment of age-related chronic diseases and can also be used for other diseases. An increasing number of long-term studies on synthetic and natural compounds aim to elucidate preclinically and clinically the mechanisms underlying being healthy and prolongation of life. To delay age-related diseases and prolong the lifespan, it is necessary to take these compounds with diet or pharmaceuticals, along with detailed toxicological results. In this review, the most promising and utilised compounds will be highlighted and it will be discussed whether they have toxic effects in short/long-term use, although they are thought to be used safely.

Vegetables and Their Bioactive Compounds as Anti-Aging Drugs

Aging is a continuous process over time that is mainly related to natural alterations in mechanical–biological processes. This phenomenon is due to several factors, including the time and energy of biological processes. Aging can be attributed to biological factors such as oxidative stress, cell longevity, and stem cell senescence. Currently, aging is associated with several diseases, such as neurodegenerative diseases, cancer, and other diseases related to oxidative stress. In addition, certain natural molecules, including those derived from vegetables, have shown the ability to delay the aging process. Their effects are linked to different mechanisms of action, such as tissue regeneration and the activation of longevity and anti-senescence genes. The present work discusses the impact of vegetables, and bioactive compounds isolated from vegetables, against the physiological and pathological aging process and accompanying human diseases.

Comparison of multi-tissue aging between human and mouse

With the rapid growth of the aging population, exploring the biological basis of aging and related molecular mechanisms has become an important topic in modern scientific research. Aging can cause multiple organ function attenuations, leading to the occurrence and development of various age-related metabolic, nervous system, and cardiovascular diseases. In addition, aging is closely related to the occurrence and development of tumors. Although a number of studies have used various mouse models to study aging, further research is needed to associate mouse and human aging at the molecular level. In this paper, we systematically assessed the relationship between human and mouse aging by comparing multi-tissue age-related gene expression sets. We compared 18 human and mouse tissues, and found 9 significantly correlated tissue pairs. Functional analysis also revealed some terms related to aging in human and mouse. And we performed a crosswise comparison of homologous age-related genes with 18 tissues in human and mouse respectively, and found that human Brain_Cortex was significantly correlated with Brain_Hippocampus, which was also found in mouse. In addition, we focused on comparing four brain-related tissues in human and mouse, and found a gene-GFAP-related to aging in both human and mouse.

Fibrodysplasia Ossificans Progressiva (FOP): A Segmental Progeroid Syndrome

Segmental progeroid syndromes are commonly represented by genetic conditions which recapitulate aspects of physiological aging by similar, disparate, or unknown mechanisms. Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disease caused by mutations in the gene for ACVR1/ALK2 encoding Activin A receptor type I/Activin-like kinase 2, a bone morphogenetic protein (BMP) type I receptor, and results in the formation of extra-skeletal ossification and a constellation of others features, many of which resemble accelerated aging. The median estimated lifespan of individuals with FOP is approximately 56 years of age. Characteristics of precocious aging in FOP include both those that are related to dysregulated BMP signaling as well as those secondary to early immobilization. Progeroid features that may primarily be associated with mutations in ACVR1 include osteoarthritis, hearing loss, alopecia, subcutaneous lipodystrophy, myelination defects, heightened inflammation, menstrual abnormalities, and perhaps nephrolithiasis. Progeroid features that may secondarily be related to immobilization from progressive heterotopic ossification include decreased vital capacity, osteoporosis, fractures, sarcopenia, and predisposition to respiratory infections. Some manifestations of precocious aging may be attributed to both primary and secondary effects of FOP. At the level of lesion formation in FOP, soft tissue injury resulting in hypoxia, cell damage, and inflammation may lead to the accumulation of senescent cells as in aged tissue. Production of Activin A, platelet-derived growth factor, metalloproteinases, interleukin 6, and other inflammatory cytokines as part of the senescence-associated secretory phenotype could conceivably mediate the initial signaling cascade that results in the intense fibroproliferative response as well as the tissue-resident stem cell reprogramming leading up to ectopic endochondral bone formation. Consideration of FOP as a segmental progeroid syndrome offers a unique perspective into potential mechanisms of normal aging and may also provide insight for identification of new targets for therapeutic interventions in FOP.

Absence of premature senescence in Werner's syndrome keratinocytes

Werner's syndrome (WS) is an autosomal recessive genetic disorder caused by loss of function mutation in wrn and is a useful model of premature in vivo ageing. Cellular senescence is a plausible causal mechanism of mammalian ageing and, at the cellular level, WS fibroblasts show premature senescence resulting from a combination of telomeric attrition and replication fork stalling. Over 90% of WS fibroblast cultures achieve <20 population doublings (PD) in vitro compared to wild type human fibroblast cultures. It has been proposed that some cell types, capable of proliferation, will fail to show a premature senescence phenotype in response to wrn mutations. To test this hypothesis, human dermal keratinocytes (derived from both WS and wild type patients) were cultured long term. WS Keratinocytes showed a replicative lifespan in excess of 100 population doublings but maintained functional growth arrest mechanisms based on p16 and p53. The karyotype of the cells was superficially normal and the cultures retained markers characteristic of keratinocyte holoclones (stem cells) including p63 expression and telomerase activity. Accordingly we conclude that, in contrast to WS fibroblasts, WS keratinocytes do not demonstrate slow growth rates or features of premature senescence. These findings suggest that the epidermis is among the tissue types that do not display symptoms of premature ageing caused by loss of function of wrn. This is in support that Werner's syndrome is a segmental progeroid syndrome.

Arterial aging: pathophysiological principles

In the nineteenth century, prior to the introduction of the cuff sphygmomanometer, arteriosclerosis (stiffening of arteries) was recognized by clinicians and by life insurance companies as an indicator of vascular aging and cardiovascular risk, even in asymptomatic individuals. Through the twentieth century, views on aging came to focus on values of systolic and diastolic pressure and on obstructive atherosclerotic disease. Such focus deflected attention from the primary aging change which occurs in all societies, and is represented by stiffening and dilation of the proximal aorta. This review emphasizes the cushioning function of elastic arteries — principally the aorta — and how in youth this results in optimal interaction with the heart, and optimal steady flow through peripheral resistance vessels. Aortic stiffening with age is principally due to fatigue and fracture of elastin lamellae, with transfer of stress to stiffer collagenous components. Stiffening increases left ventricular load and myocardial blood requirement, but limits the capacity for blood supply during diastole. Consequences are cardiac failure and predisposition to ischaemia. The second, under-appreciated effect of aortic stiffening is transmission of flow pulsations downstream into vasodilated organs, principally brain and kidney, where pulsatile energy is dissipated and fragile microvessels are damaged. This accounts for micro infarcts and microhaemorrhages, with specialized cell damage, cognitive decline and renal failure. The aging process can be best monitored by change in the arterial pressure wave rather than by reliance on the cuff sphygmomanometer. This reintroduces the approaches by clinicians and life insurance examiners of the nineteenth century, endorses modern treatments for established disease, and holds the promise of detecting premature arterial degeneration, and better applying lifestyle measures and vasoactive medications to modify the aging process.

Lifespan and aggregate size variables in specifications of mortality or survivorship

A specification of mortality or survivorship provides respective explicit details about mortality's or survivorship's relationships with one or more other variables (e.g., age, sex, etc.). Previous studies have discovered and analyzed diverse specifications of mortality or survivorship; these discoveries and analyses suggest that additional specifications of mortality or survivorship have yet to be discovered and analyzed. In consistency with previous research, multivariable limited powered polynomials regression analyses of mortality and survivorship of selected humans (Swedes, 1760-2008) and selected insects (caged medflies) show age-specific, historical-time-specific, environmental-context-specific, and sex-specific mortality and survivorship. These analyses also present discoveries of hitherto unknown lifespan-specific, contemporary-aggregate-size-specific, and lifespan-aggregate-size-specific mortality and survivorship. The results of this investigation and results of previous research help identify variables for inclusion in regression models of mortality or survivorship. Moreover, these results and results of previous research strengthen the suggestion that additional specifications of mortality or survivorship have yet to be discovered and analyzed, and they also suggest that specifications of mortality and survivorship indicate corresponding specifications of frailty and vitality. Furthermore, the present analyses reveal the usefulness of a multivariable limited powered polynomials regression model-building approach. This article shows that much has yet to be learned about specifications of mortality or survivorship of diverse kinds of individuals in diverse times and places.

Species with a chemical defence, but not chemical offence, live longer

Evolutionary hypotheses for ageing generally predict that delayed senescence should evolve in organisms that experience lower extrinsic mortality. Thus, one might expect species that are highly toxic or venomous (i.e. chemically protected) will have longer lifespans than related species that are not likewise protected. This remarkable relationship has been suggested to occur in amphibians and snakes. First, we show that chemical protection is highly conserved in several lineages of amphibians and snakes. Therefore, accounting for phylogenetic autocorrelation is critical when conservatively testing evolutionary hypotheses because species may possess similar longevities and defensive attributes simply through shared ancestry. Herein, we compare maximum longevity of chemically protected and nonprotected species, controlling for potential nonindependence of traits among species using recently available phylogenies. Our analyses confirm that longevity is positively correlated with body size in both groups which is consistent with life-history theory. We also show that maximum lifespan was positively associated with chemical protection in amphibian species but not in snakes. Chemical protection is defensive in amphibians, but primarily offensive (involved in prey capture) in snakes. Thus, we find that although chemical defence in amphibians favours long life, there is no evidence that chemical offence in snakes does the same.

Hedgehog signalling as an antagonist of ageing and its associated diseases

Hedgehog is an important morphogenic signal that directs pattern formation during embryogenesis, but its activity also remains present through adult life. It is now becoming increasingly clear that during the reproductive phase of life and beyond it continues to direct cell renewal (which is essential to combat the chronic environmental stress to which the body is constantly exposed) and counteracts vascular, osteolytic and sometimes oncological insults to the body. Conversely, down-regulation of hedgehog signalling is associated with ageing-related diseases such as type 2 diabetes, neurodegeneration, atherosclerosis and osteoporosis. Hence, in this essay we argue that hedgehog signalling is not only important at the start of life, but also constitutes an important anti-geriatric influence, and that enhanced understanding of its properties may contribute to developing rational strategies for healthy ageing and prevention of ageing-related diseases.

Heterogeneity in the Strehler-Mildvan general theory of mortality and aging

This study examines and further develops the classic Strehler-Mildvan (SM) general theory of mortality and aging. Three predictions from the SM theory are tested by examining the age dependence of mortality patterns for 42 countries (including developed and developing countries) over the period 1955-2003. By applying finite mixture regression models, principal component analysis, and random-effects panel regression models, we find that (1) the negative correlation between the initial adulthood mortality rate and the rate of increase in mortality with age derived in the SM theory exists but is not constant; (2) within the SM framework, the implied age of expected zero vitality (expected maximum survival age) also is variable over time; (3) longevity trajectories are not homogeneous among the countries; (4) Central American and Southeast Asian countries have higher expected age of zero vitality than other countries in spite of relatively disadvantageous national ecological systems; (5) within the group of Central American and Southeast Asian countries, a more disadvantageous national ecological system is associated with a higher expected age of zero vitality; and (6) larger agricultural and food productivities, higher labor participation rates, higher percentages of population living in urban areas, and larger GDP per capita and GDP per unit of energy use are important beneficial national ecological system factors that can promote survival. These findings indicate that the SM theory needs to be generalized to incorporate heterogeneity among human populations.

Welfare of Aged Horses

Simple Summary

Horses form a unique and special part of their owners' lives and aged horses are no exception. This review considers the health and management of aged horses. In particular how owners manage and care for their aged horses, what diseases and conditions they suffer from and what factors affect their quality of life. As an aged horse reaches the end of its life, an owner will be faced with judging its quality of life and making the decision to end its suffering. The veterinary surgeon plays an essential role in supporting the owner in this process.

Abstract

Horses form a unique and special part of their owners' lives and aged horses are no exception. This review considers the health and management of aged horses, including the role of the owner and their perceptions of aged horses, potential threats or risks to their welfare and finally, factors affecting quality of life and euthanasia of aged horses. Owners of aged horses are concerned about the health, welfare and quality of life of their aged animals. Yet surveys of management and preventive healthcare reflect that there may be some limitations to what owners are actually achieving in practice. They show declining management as horses age, particularly for the retired horse and insufficient appropriate preventive healthcare via veterinary surgeons. The veterinary surgeon plays an essential and influential role in preventive healthcare, management of diseases and disorders and ultimately in the decision making process for euthanasia of aged horses at the end of their lives. The value of aged horses should not be underestimated by veterinarians and others working with them and the continuing care of aged horses should be regarded with the same importance as the care of younger horses with more obvious monetary value.

Suitability of the clonal marbled crayfish for biogerontological research: a review and perspective, with remarks on some further crustaceans

This article examines the suitability of the parthenogenetic marbled crayfish for research on ageing and longevity. The marbled crayfish is an emerging laboratory model for development, epigenetics and toxicology that produces up to 400 genetically identical siblings per batch. It is easily cultured, has an adult size of 4-9 cm, a generation time of 6-7 months and a life span of 2-3 years. Experimental data and biological peculiarities like isogenicity, direct development, indeterminate growth, high regeneration capacity and negligible senescence suggest that the marbled crayfish is particularly suitable to investigate the dependency of ageing and longevity from non-genetic factors such as stochastic developmental variation, allocation of metabolic resources, damage and repair, caloric restriction and social stress. It is also well applicable to examine alterations of the epigenetic code with increasing age and to identify mechanisms that keep stem cells active until old age. As a representative of the sparsely investigated crustaceans and of animals with indeterminate growth and extended brood care the marbled crayfish may even contribute to evolutionary theories of ageing and longevity. Some relatives are recommended as substitutes for investigation of topics, for which the marbled crayfish is less suitable like genetics of ageing and achievement of life spans of decades under conditions of low food and low temperature. Research on ageing in the marbled crayfish and its relatives is of practical relevance for crustacean fisheries and aquaculture and may offer starting points for the development of novel anti-ageing interventions in humans.

Testing evolutionary theories of menopause

Why do women cease fertility rather abruptly through menopause at an age well before generalized senescence renders child rearing biologically impossible? The two main evolutionary hypotheses are that menopause serves either (i) to protect mothers from rising age-specific maternal mortality risks, thereby protecting their highly dependent younger children from death if the mother dies or (ii) to provide post-reproductive grandmothers who enhance their inclusive fitness by helping to care and provide for their daughters' children. Recent theoretical work indicates that both factors together are necessary if menopause is to provide an evolutionary advantage. However, these ideas need to be tested using detailed data from actual human life histories lived under reasonably 'natural' conditions; for obvious reasons, such data are extremely scarce. We here describe a study based on a remarkably complete dataset from The Gambia. The data provided quantitative estimates for key parameters for the theoretical model, which were then used to assess the actual effects on fitness. Empirically based numerical analysis of this nature is essential if the enigma of menopause is to be explained satisfactorily in evolutionary terms. Our results point to the distinctive (and perhaps unique) role of menopause in human evolution and provide important support for the hypothesized evolutionary significance of grandmothers.

The proteasome and intracellular redox status: implications for apoptotic regulation in lens epithelial cells

PURPOSE

This study aimed to investigate redox regulation of the proteasome as well as the effect of proteasome inhibition on intracellular oxidative status and apoptosis.

METHODS

Oxidative stress was induced in cultured human lens epithelial cells (HLECs) and intact mouse lenses by 100 microM H2O2. HLECs were also exposed to the reduced and the oxidized forms of glutathione (GSH/GSSG) and the reducing agent dithiotreitol (DTT). The chymotrypsin-like, the trypsin-like, and the peptidylglutamyl peptidase activities of the proteasome were measured using synthetic fluorogenic substrates. Superoxide as well as peroxide production, mitochondrial membrane potential, and the level of GSH was measured in HLECs after proteasome inhibition by MG-132 or lactacystin. Apoptosis was determined by measuring caspase-3 activation and by studying apoptotic nuclei after staining with Hoechst 33342.

RESULTS

All three peptidase activities of the proteasome were inhibited by 100 microM H2O2 and by the oxidized form of glutathione (GSSG), whereas the reduced form (GSH) stimulated chymotrypsin-like and peptidylglutamyl peptidase activities in HLECs lysates. Intact mouse lenses exposed to 100 microM H2O2 exhibited loss of transparency and trends of decreased chymotrypsin-like proteasome activity as well as decreased GSH levels. Inhibition of the proteasome in cultured HLECs caused significant increase in apoptosis and disturbed intracellular redox balance. Simultaneous addition of exogenous GSH completely abolished the increased apoptosis seen after MG-132 treatment.

CONCLUSIONS

This study supports the hypothesis that intracellular proteolytic and oxidative regulatory systems are tightly coupled. The current data also indicate that apoptosis by proteasome inhibition is mediated through oxidative mechanisms.

Hallmarks of telomeres in ageing research

Telomeres are repetitive DNA sequences at the ends of linear chromosomes. Telomerase, a cellular reverse transcriptase, helps maintain telomere length in human stem cells, reproductive cells and cancer cells by adding TTAGGG repeats onto the telomeres. However, most normal human cells do not express telomerase and thus each time a cell divides some telomeric sequences are lost. When telomeres in a subset of cells become short (unprotected), cells enter an irreversible growth arrest state called replicative senescence. Cells in senescence produce a different constellation of proteins compared to normal quiescent cells. This may lead to a change in the homeostatic environment in a tissue-specific manner. In most instances cells become senescent before they can become cancerous; thus, the initial growth arrest induced by short telomeres may be thought of as a potent anti-cancer protection mechanism. When cells can be adequately cultured until they reach telomere-based replicative senescence, introduction of the telomerase catalytic protein component (hTERT) into telomerase-silent cells is sufficient to restore telomerase activity and extend cellular lifespan. Cells with introduced telomerase are not cancer cells, since they have not accumulated the other changes needed to become cancerous. This indicates that telomerase-induced telomere length manipulations may have utility for tissue engineering and for dissecting the molecular mechanisms underlying genetic diseases, including cancer.

From old organisms to new molecules: integrative biology and therapeutic targets in accelerated human ageing

Understanding the basic biology of human ageing is a key milestone in attempting to ameliorate the deleterious consequences of old age. This is an urgent research priority given the global demographic shift towards an ageing population. Although some molecular pathways that have been proposed to contribute to ageing have been discovered using classical biochemistry and genetics, the complex, polygenic and stochastic nature of ageing is such that the process as a whole is not immediately amenable to biochemical analysis. Thus, attempts have been made to elucidate the causes of monogenic progeroid disorders that recapitulate some, if not all, features of normal ageing in the hope that this may contribute to our understanding of normal human ageing. Two canonical progeroid disorders are Werner's syndrome and Hutchinson-Gilford progeroid syndrome (also known as progeria). Because such disorders are essentially phenocopies of ageing, rather than ageing itself, advances made in understanding their pathogenesis must always be contextualised within theories proposed to help explain how the normal process operates. One such possible ageing mechanism is described by the cell senescence hypothesis of ageing. Here, we discuss this hypothesis and demonstrate that it provides a plausible explanation for many of the ageing phenotypes seen in Werner's syndrome and Hutchinson-Gilford progeriod syndrome. The recent exciting advances made in potential therapies for these two syndromes are also reviewed.

SIRT1: linking adaptive cellular responses to aging-associated changes in organismal physiology

Sirtuins comprise a family of enzymes implicated in the determination of organismal life span in yeast and the nematode. The mammalian sirtuin SIRT1 has been shown to deacetylate several proteins in an NAD(+)-dependent manner. SIRT1 substrates are involved in the regulation of apoptosis/cell survival, endocrine signaling, differentiation, chromatin remodeling, and transcription. Thus SIRT1 provides a molecular link between nutrient availability and adaptive transcriptional responses. This review presents current evidence as to how SIRT1 functions are relevant to changes in tissue physiology that occur with ageing and its implications for future pharmacological intervention to alleviate such degenerative processes.

Oxidative stress and ageing: is ageing a cysteine deficiency syndrome?

Reactive oxygen species (ROS) are constantly produced in biological tissues and play a role in various signalling pathways. Abnormally high ROS concentrations cause oxidative stress associated with tissue damage and dysregulation of physiological signals. There is growing evidence that oxidative stress increases with age. It has also been shown that the life span of worms, flies and mice can be significantly increased by mutations which impede the insulin receptor signalling cascade. Molecular studies revealed that the insulin-independent basal activity of the insulin receptor is increased by ROS and downregulated by certain antioxidants. Complementary clinical studies confirmed that supplementation of the glutathione precursor cysteine decreases insulin responsiveness in the fasted state. In several clinical trials, cysteine supplementation improved skeletal muscle functions, decreased the body fat/lean body mass ratio, decreased plasma levels of the inflammatory cytokine tumour necrosis factor alpha (TNF-alpha), improved immune functions, and increased plasma albumin levels. As all these parameters degenerate with age, these findings suggest: (i) that loss of youth, health and quality of life may be partly explained by a deficit in cysteine and (ii) that the dietary consumption of cysteine is generally suboptimal and everybody is likely to have a cysteine deficiency sooner or later.

Oxidative Aging and Insulin Receptor Signaling

The life span of nematodes, fruit flies, and mice can be significantly increased (and aging-related changes decreased) by mutations affecting insulin receptor signaling. This effect involves several cellular functions which are negatively regulated by the insulin receptor and thus typically expressed under fasting conditions. This involvement raises the question of whether the insulin-independent basal receptor kinase activity in the postabsorptive state can be decreased without compromising the physiologically important response to insulin in the postprandial state. Recent studies have shown that (a) the basal human insulin receptor kinase activity is increased under oxidative conditions in the absence of insulin and (b) insulin signaling in the fasted state can be decreased by cysteine supplementation. Cysteine supplementation has also been shown to improve certain aging-related parameters, suggesting that the average dietary cysteine consumption in Western countries may be suboptimal. These findings provide a conceptual framework that extends the "free radical theory of aging."

Starvation in humans: Evolutionary background and contemporary implications

Although there is extensive evidence that caloric restriction (CR) extends lifespan in several species the evidence base for humans is weak. We are still at the stage of applying inductive reasoning and of framing hypotheses to be tested. It is known that a genetic background contributes about 25% to the variation in human longevity, but thought unlikely that any genes conferring longer lifespan have been positively selected to do so. It is more likely that any such benefits are unintended consequences arising from other adaptations. If there is an association between CR and longevity in humans it may have been selected by previous exposures to famine. This paper briefly reviews the historical evidence on the extent and frequency of famines in human history. It is concluded that starvation has been one of the major selective pressures on the human genome and has left abundant evidence of adaptive survival traits. Many of these are mediated through effects on reproduction. However, interpretation of the possible links between these energy-sparing mechanisms and any association between CR and ageing is handicapped by an absence of data on the latter and will remain a matter of debate for many years to come.

Maximum longevities of chemically protected and non-protected fishes, reptiles, and amphibians support evolutionary hypotheses of aging

Evolutionary hypotheses of aging predict that species with low rates of mortality from extrinsic sources, such as predation, should senesce more slowly and have longer maximum life spans than related species with higher rates of extrinsic mortality. We tested this prediction by synthesizing information on maximum body lengths and life spans in captivity of 1193 species of chemically protected (venomous or poisonous) and non-chemically protected fishes, snakes, caudatans (salamanders and newts), and anurans (frogs and toads). In every phylogenetic group maximum longevity was positively correlated with body size and, when size was controlled for statistically, chemically protected species and genera usually had longer maximum life spans than non-protected species. These results reemphasize the importance of life history traits, particularly protection from predation, in the evolution of senescence.

Hérédité et longévité au Québec ancien*

Par l’entremise du Registre de la population du Québec ancien (RPQA), banque de données élaborée dans le cadre du Programme de recherche en démographie historique, nous avons observé l’existence d’une composante familiale de la longévité. En effet, l’âge au décès des parents semble influencer l’âge au décès de leurs fils et filles, particulièrement pour les parents décédés après 70 ans. Nous avons aussi observé une convergence significative de l’âge au décès dans les fratries. Cependant, il existe également une relation entre les âges au décès des conjoints, ce qui laisse supposer que la composante familiale est due à la part environnementale de l’héritabilité plutôt qu’à la part génétique.

Variation in the human TP53 gene affects old age survival and cancer mortality

Longevity may depend on a balance between tumor suppression and tissue renewal mechanisms [Campisi, J., 2003. Cancer and ageing: rival demons? Nat. Rev. Cancer 3 (5), 339-349]. Mice with constitutively activated p53 are almost cancer free but their life span is reduced and accompanied by early tissue atrophy [Tyner et al., 2002. p53 mutant mice that display early ageing-associated phenotypes. Nature 415 (6867) 45-53]. Replacement of arginine (Arg) by proline (Pro) at position 72 of human p53 decreases its apoptotic potential [Dumont et al., 2003. The codon 72 polymorphic variants of p53 have markedly different apoptotic potential. Nat. Genet. 33 (3), 357-365] providing a tool to test for a similar trade-off in humans. Using a formal meta-analysis of the published literature we show that carriers of the TP53 codon 72 Pro/Pro genotype have an increased cancer risk compared to Arg/Arg carriers (p<0.05). Next, in a prospective study of 1226 people aged 85 years and over we show that carriers of the Pro/Pro genotype have a 41% increased survival (p = 0.032) despite a 2.54 fold increased (p = 0.007) proportional mortality from cancer. It is suggested that human p53 protect against cancer but at a cost of longevity.

What can progeroid syndromes tell us about human aging?

Human genetic diseases that resemble accelerated aging provide useful models for gerontologists. They combine known single-gene mutations with deficits in selected tissues that are reminiscent of changes seen during normal aging. Here, we describe recent progress toward linking molecular and cellular changes with the phenotype seen in two of these disorders. One in particular, Werner syndrome, provides evidence to support the hypothesis that the senescence of somatic cells may be a causal agent of normal aging.

Humoral immune response in relation to senescence, sex and sexual ornamentation in the barn swallow (Hirundo rustica)

Performance of animals may decline with age. The effects of senescence, however, may differ between the sexes because of differences in physiology and behaviour. Acquired immunity provides hosts with efficient mechanisms of anti-parasite defence, but the effect of senescence on immunocompetence has never been studied in natural populations. In the barn swallow (Hirundo rustica), primary antibody response to an antigen during one breeding season declined with age in females, while secondary response during the following breeding season declined with age in both sexes. Parasite-mediated sexual selection theory posits that male secondary sexual characters reveal resistance to parasites. Males with large tail ornaments had stronger primary response, retained larger antibody levels until the following year, but did not differ in secondary response compared with short-tailed males, as predicted if ornamentation reflects resistance to parasites. This is the first study showing that immunocompetence declines with age in any vertebrate under natural conditions.

Aging-related changes in the thiol/disulfide redox state: implications for the use of thiol antioxidants

Genetic and biochemical studies suggest that free radical-derived reactive oxygen species play a key role in a common mechanism of aging in many or all animal species. This led to the hypothesis that the quality of life in old age may be improved by pharmacological or dietary thiol antioxidants. This review describes important details about how the organism deals with its own thiol antioxidants. Aging was found to be associated with an oxidative shift in the thiol/disulfide redox state (REDST) of the intracellular glutathione pool and of the plasma cyst(e)ine and albumin pools. There is also a decrease in plasma thiol (mainly cysteine) concentration. The oxidative shift in intracellular REDST was found to be typically associated with cellular dysfunctions. Studies in humans related to plasma REDST revealed correlations with aging-related pathophysiological processes, suggesting that oxidative changes in REDST play a key role in processes and diseases which limit the human life span. The age-related shift in plasma REDST is mediated, at least partly, by the decreasing capacity to remove dietary cysteine from the oxidative environment of the blood. Thiol antioxidants were found to ameliorate various aging-related processes but obviously ought to be used with caution in consideration of the oxidative environment of the blood.

Stochastic and genetic factors influence tissue-specific decline in ageing C. elegans

The nematode Caenorhabditis elegans is an important model for studying the genetics of ageing, with over 50 life-extension mutations known so far. However, little is known about the pathobiology of ageing in this species, limiting attempts to connect genotype with senescent phenotype. Using ultrastructural analysis and visualization of specific cell types with green fluorescent protein, we examined cell integrity in different tissues as the animal ages. We report remarkable preservation of the nervous system, even in advanced old age, in contrast to a gradual, progressive deterioration of muscle, resembling human sarcopenia. The age-1(hx546) mutation, which extends lifespan by 60-100%, delayed some, but not all, cellular biomarkers of ageing. Strikingly, we found strong evidence that stochastic as well as genetic factors are significant in C. elegans ageing, with extensive variability both among same-age animals and between cells of the same type within individuals.

The regulatory anatomy of honeybee lifespan

Honeybee workers (Apis mellifera) may be classified as either short-lived summer bees or long-lived winter bees in temperate zones. The protein status appears to be a major determinant of honeybee lifespan, and the lipoprotein vitellogenin seems to play a crucial role. Here, we give a review of the role of the vitellogenin in honeybee workers, and present a data-driven mathematical model describing the dynamics of this representative protein in the individual bee as a function of its task profile under various regimes. The results support the hypothesis that vitellogenin is a true storage protein that is utilized for various metabolic purposes including the synthesis of brood food. Except for workers having been foragers for many days, they also suggest that the previous life histories of workers do not constrain them from becoming winter bees as long as they get ample food and time to build up their protein reserves before wintering. The results also indicate that it may not be necessary to introduce the ovary as a storage organ for vitellogenin in order to generate normal winter bees. The insights gained from these results are then discussed in a broader gerontological and life history context. Remarkably similar features concerning regulation of ageing in Caenorhabditis elegans, Drosophila melanogaster and honeybees are pointed out and discussed. Furthermore, we show that in contrast to the "mutation accumulation" and the "antagonistic pleiotropy" evolutionary theories of ageing, the "disposable soma" theory is capable of explaining the bimodal longevity distribution of honeybees when interpreted in a group selection context. Finally, by showing that depletion of nutrient stores can be actively controlled by pathways connected to regulation of ageing, we strengthen the claim that age-based division of labour, with performance of risky tasks delayed until late in life by workers with depleted nutrient stores, may have evolved as an energy-saving mechanism in insect colonies.

Evolution of ageing

Explaining why ageing occurs is a solution to the longstanding enigma of the role of senescence in nature. Even after half a century of progress, this solution continues to unfold. Evolution theory argues strongly against programmed ageing, suggesting instead that organisms are programmed for survival, not death. In the current view, ageing results from the twin principles that (i) the force of natural selection declines with age, and (ii) longevity requires investments in somatic maintenance and repair that must compete against investments in growth, reproduction and activities that might enhance fitness. In addition to explaining why ageing occurs, the evolutionary theory also provides insight into the mechanisms underlying the complex cellular and molecular changes that contribute to senescence, as well as an array of testable predictions. Some of the most interesting current problems are to understand how the genetic factors influencing ageing and longevity are predicted to respond to fluctuating environments, such as temporary periods of famine, as well as to other kinds of spatial and/or temporal heterogeneity. Rapid progress in human genomics raises the prospect of greatly increasing our knowledge of the determinants of human longevity. To make progress in understanding the role and evolution of genetic and non-genetic factors in human longevity, we need more detailed theoretical studies of how intra-population variables, such as socio-economic status, influence the selection forces that shape the life history.

New age patterns of survival improvement in Sweden: do they characterize changes in individual aging?

The parameters of the Gompertz approximation to the mortality curve are negatively correlated. Strehler and Mildvan [Science 132 (1960) 14] predicted this property of the mortality curve using a mathematical model of mortality and aging and then confirmed it in empirical studies. Despite the fact that their theory was based on the cohort model of mortality the SM correlation was also revealed in the analysis of period mortality data. In fact, most applications of the SM model to human data use Gompertz's approximation to the period mortality rate. Many researchers studying SM correlation consider it a universal demographic law. Such correlation prescribes a certain regularity in mortality changes. All mortality curves must intersect at one point. Mortality decline must produce the rectangularization of survival curves. In this paper we investigated the changes in the patterns of mortality decline in Sweden between 1861 and 1999. We found a difference in patterns of SM correlation for cohort and period mortality data. We investigated trends in survival improvement and found that the tendency to rectangularization of the survival curve existed for only a limited period of time. Then it was gradually replaced by near parallel shift of the survival curve to the right. We found that the pattern of SM correlation was relatively stable only at certain phases of the survival history of male and female populations. We analyzed past and recent patterns of survival changes and discussed possible causes for instability of SM correlation both in cohort and in period mortality data.

A model for the phenotypic presentation of Werner's syndrome

Werner's syndrome (WS) is a valuable model of accelerated ageing and results from mutations in a recQ helicase (wrn). WS fibroblasts show a mutator phenotype, replication fork stalling, increased rates of mean telomeric loss and accelerated cellular senescence. Senescence has been proposed as a candidate mechanism for the ageing of mitotic tissue. However, some mitotic tissues (such as the immune system) seem unaffected in WS. Is this evidence against a role for cell senescence in ageing? Two experiments resolve this paradox (i) the demonstration that the abbreviated replicative lifespan of WS fibroblasts can be corrected by the ectopic expression of telomerase and (ii) the demonstration that T cells derived from WS patients have the mutator phenotype characteristic of the disease but show no reduction in replicative potential. Since T cells can upregulate telomerase naturally these findings are consistent with a model in which the only wrn-mediated deletions that have a significant effect on replicative lifespan are those at or near the telomere. These data are thus supportive of a role for senescence in the ageing of the immune system. Emerging data on divisional counting mechanisms have the potential to produce many other apparent WS "paradoxes". Accordingly, we propose a general model for the phenotypic presentation of WS, which includes a modification of the Olovnikov model of telomere erosion. Somewhat unexpectedly, this predicts that accelerated senescence should not be observed in all telomerase-negative WS cell types.

A stochastic model of cell replicative senescence based on telomere shortening, oxidative stress, and somatic mutations in nuclear and mitochondrial DNA

Human diploid fibroblast cells can divide for only a limited number of times in vitro, a phenomenon known as replicative senescence or the Hayflick limit. Variability in doubling potential is observed within a clone of cells, and between two sister cells arising from a single mitotic division. This strongly suggests that the process by which cells become senescent is intrinsically stochastic. Among the various biochemical mechanisms that have been proposed to explain replicative senescence, particular interest has been focussed on the role of telomere reduction. In the absence of telomerase--an enzyme switched off in normal diploid fibro-blasts-cells lose telomeric DNA at each cell division. According to the telomere hypothesis of cell senescence, cells eventually reach a critically short telomere length and cell cycle arrest follows. In support of this concept, forced expression of telomerase in normal fibroblasts appears to prevent cell senescence. Nevertheless, the telomere hypothesis in its basic form has some difficulty in explaining the marked stochastic variations seen in the replicative lifespans of individual cells within a culture, and there is strong empirical and theoretical support for the concept that other kinds of damage may contribute to cellular ageing. We describe a stochastic network model of cell senescence in which a primary role is played by telomere reduction but in which other mechanisms (oxidative stress linked particularly to mitochondrial damage, and nuclear somatic mutations) also contribute. The model gives simulation results that are in good agreement with published data on intra-clonal variability in cell doubling potential and permits an analysis of how the various elements of the stochastic network interact. Such integrative models may aid in developing new experimental approaches aimed at unravelling the intrinsic complexity of the mechanisms contributing to human cell ageing.

Have the oldest old adults ever been frail in the past? A hypothesis that explains modern trends in survival

Three important results concerning the shape and the trends of the human mortality rate were discussed recently in demographic and epidemiological literature. These are the deceleration of the mortality rate at old ages, the tendency to rectangularization of the survival curve, and the decline of the old age mortality observed in the second part of the 20th century. In this paper we show that all these results can be explained by using a model with a new type of heterogeneity associated with individual differences in adaptive capacity. We first illustrate the idea of such a model by considering survival in a mixture of two subpopulations of individuals (called "labile" and "stable"). These subpopulations are characterized by different Gompertz mortality patterns, such that their mortality rates cross over. The survival chances of individuals in these subpopulations have different sensitivities to changes in environmental conditions. Then we develop a more comprehensive model in which the mortality rate is related to the adaptive capacity of an organism. We show that the trends in survival patterns experienced by a mixture of such individuals resemble those obtained in an analysis of empirical data on survival in developed countries. Lastly, we present evidence of the existence of subpopulations of phenotypes in both humans and experimental organisms, which were used as prototypes in our models. The existence of such phenotypes provides the possibility that at least part of today's centenarians originated from an initially frail part of the cohort.

Stress, DNA damage and ageing -- an integrative approach

Ageing is highly complex, involving multiple mechanisms at different levels. Nevertheless, recent evidence suggests that several of the most important mechanisms are linked via endogenous stress-induced DNA damage caused by reactive oxygen species (ROS). Understanding how such damage contributes to age-related changes requires that we explain how these different mechanisms relate to each other and potentially interact. In this article, we review the contributions of stress-induced damage to cellular DNA through (i) the role of damage to nuclear DNA and its repair mediated via the actions of poly(ADP-ribose) polymerase-1, (ii) the role of damage to telomeric DNA and its contribution to telomere-driven cell senescence, and (iii) the role of damage to and the accumulation of mutations in mitochondrial DNA. We describe how an integrative approach to studying these mechanisms, coupled with computational modelling, may be of considerable importance in resolving some of the complexity of cellular ageing.

Sex and ageing

Sex and ageing are often linked, particularly in the context of the evolutionary theories of ageing, which suggest that senescence may be the price for investing in offspring at the expense of somatic maintenance and repair. Considerable evidence supports this concept although, strictly, it is not sex per se but the existence of the soma/germ-line distinction that appears to hold the key. Other aspects of the sex-ageing axis seeing exciting new developments are the evolution of the human life history, particularly with respect to menopause, and the molecular mechanisms that sustain the immortality of the germ-line in contrast to the cumulative damage that appears to underlie the ageing of somatic cells.

Evolution of the human menopause

Menopause is an evolutionary puzzle since an early end to reproduction seems contrary to maximising Darwinian fitness. Several theories have been proposed to explain why menopause might have evolved, all based on unusual aspects of the human life history. One theory is that menopause follows from the extreme altriciality of human babies, coupled with the difficulty in giving birth due to the large neonatal brain size and the growing risk of child-bearing at older ages. There may be little advantage for an older mother in running the increased risk of a further pregnancy when existing offspring depend critically on her survival. An alternative theory is that within kin groups menopause enhances fitness by producing post-reproductive grandmothers who can assist their adult daughters. Such theories need careful quantitative assessment to see whether the fitness benefits are sufficient to outweigh the costs, particularly in circumstances of relatively high background mortality typical of ancestral environments. We show that individual theories fail this test, but that a combined model incorporating both hypotheses can explain why menopause may have evolved.

Telomeres, replicative senescence and human ageing

Ageing concerns the extracellular environment and cells that are either post-mitotic or capable of division during life. Primary human cells have a finite division capacity in culture before they enter a state of viable cell cycle arrest termed senescence. Cell division occurs during life in many tissues, either as part of normal tissue function or in response to tissue damage. The accumulation of cells at the end of their replicative lifespan in the elderly might contribute to aged tissue either because of a reduced ability to undergo proliferation or because of the known altered gene-expression patterns of senescent cells. This has been illustrated experimentally using a transgenic telomerase-negative mouse, which shows some premature ageing phenotypes. The mechanism whereby cells count divisions uses the gradual erosion of the ends of chromosomes (telomeres) with cell division caused by the repression of the telomere-maintenance enzyme telomerase in most human cells. Telomere erosion ultimately triggers replicative senescence in many cell types; this can be prevented experimentally by forcibly expressing telomerase. This extends the lifespan of normal human cells and those from progeroid syndromes such as Werner's. Telomere-driven senescence did not evolve to cause ageing, but is instead a by-product of a system devised to provide a tumour-suppression function, a concept that fits well with evolutionary arguments regarding trade-offs between somatic maintenance and reproduction. Work in the future will focus on the development of new animal models to critically address the quantitative significance of this ageing mechanism.

Why do we age?

The evolutionary theory of ageing explains why ageing occurs, giving valuable insight into the mechanisms underlying the complex cellular and molecular changes that contribute to senescence. Such understanding also helps to clarify how the genome shapes the ageing process, thereby aiding the study of the genetic factors that influence longevity and age-associated diseases.

Review article: ageing and the neutrophil: no appetite for killing?

In the armoury of the immune system developed to combat the various micro-organisms that could invade the host, the neutrophil forms the first line of defence against rapidly dividing bacteria and fungi. However, as humans age they become more susceptible to infection with these microbes and this has been ascribed to a decline in immune status, termed immune senescence. Here we summarize the literature specifically concerning the attenuation of neutrophil function with age and the possible mechanisms underlying their reduced response to infectious agents.

Inherited variability of the mitochondrial genome and successful aging in humans

Increasing data indicate that polymorphic variants of nuclear loci can affect rate and quality of aging in humans. However, the mitochondrial genome is another good candidate, because of the central role played by mitochondrial genes in oxidative phosphorylation (OXPHOS) and cell metabolism. A characteristic of the mitochondrial genome (mtDNA) is the high level of interindividual variability that ensues from high mutation rate and unilinear inheritance. Related groups of germline/inherited mtDNA polymorphisms (haplogroups) have been identified as continent-specific sets of stable/ancient/associated restriction fragment length polymorphisms in the mtDNA coding region, representing markers capable of exactly depicting the mtDNA pool of a specific population. The hypothesis can be put forward that mtDNA variants included in a haplogroup may have similar OXPHOS efficiency and therefore act as genetic factors predisposing to individual successful or unsuccessful aging. This idea can be explored by sampling groups of individuals of different ages from a well-defined population and comparing the pools of mtDNA haplogroups between samples. The results obtained by screening mtDNA haplogroups in about 800 Italians of different ages, including more than 200 centenarians, agree with the hypothesis that the inherited variability of the mitochondrial genome is associated with the chance of successful aging and longevity in humans.

Impairment of B lymphopoiesis in precocious aging (klotho) mice

Inactivation of the klotho gene in mice results in multiple disorders that resemble human aging after 3 weeks of age. Because hematopoiesis, especially B lymphopoiesis, is affected in humans and mice by aging, we analyzed the hematopoietic state in homozygous klotho (kl/kl) mice. The kl/kl mice showed thymic atrophy and a reduced number of splenocytes. These mice had almost the normal number of myeloid cells, erythroid cells, IL-3-responsive myeloid precursors and colony forming units in spleen (CFU-S) in bone marrow (BM), but had a substantially decreased number of B cells in BM and peripheral blood as compared with wild-type mice. IL-7-responsive B cell precursors and all of the maturation stages of B cells in BM were also reduced. However, the function of hematopoietic stem cells including their capacity of B lymphopoiesis in vivo and in vitro was normal. Early B cell development was also normal in neonates and young kl/kl mice until 2 weeks old without aging phenotypes. RT-PCR analysis revealed that the level of IL-7 gene expression was significantly reduced in freshly isolated kl/kl BM cells. However, injection of IL-7 in kl/kl mice could not rescue the B lymphopenia. These findings indicate that Klotho protein may regulate B lymphopoiesis via its influence on the hematopoietic microenvironment.

Accumulation of defective mitochondria through delayed degradation of damaged organelles and its possible role in the ageing of post-mitotic and dividing cells

The mitochondrial theory of ageing proposes that an accumulation of defective mitochondria is a major contributor to the cellular deterioration that underlies the ageing process. The plausibility of the mitochondrial theory depends critically upon the population dynamics of intact and mutant mitochondria in different cell types. Earlier work suggested that mutant mitochondria might have a replication advantage but failed to account for the fact that mutants accumulate faster in post-mitotic than in dividing cells. We describe a new mathematical model that allows for damaged mitochondria to replicate more slowly, which accommodates experimental evidence of impaired energy generation and a reduced proton gradient in defective mitochondria. However, this is compensated for by a slower degradation rate of damaged mitochondria than intact ones, as suggested by de Grey (1997), which gives damaged mitochondria a selective advantage and leads to a clonal expansion of damaged mitochondria. This theoretical result is important because it agrees with evidence that, during ageing, single muscle fibres are taken over by one or only a few types of mtDNA mutants. The model also shows that cell division can rejuvenate and stabilize the mitochondrial population, consistent with data that post-mitotic tissues accumulate mitochondrial damage faster than mitotically active tissues.